EXPERIMENTAL INVESTIGATION OF FLOW PATTERN IN A SPRAY DRYER

1nvest.igation of flow pattern in a cocurrent disk spray dryer by means of measurement, of the kernel function is described. The obtained measurement results not only inform on the air flow type but ran be directly applied as input in the integral equation based simulation of heat and mass transfer.     

OBSERVATIONS OF FLOW PATTERNS IN A SPRAY DRYER

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anticlockwise and chaotic behaviour.     

OBSERVATIONS OF FLOW PATTERNS IN A SPRAY DRYER

ABSTRACT

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anticlockwise and chaotic behaviour.     

GAS FLOW BEHAVIOUR IN SPRAY DRYER

Gas flow behaviour in co-current spray dryer is investigated numerically using the k-ε model of turbulent flow.The calculated flow fields are compared with previous experimental results. The distributions of the time average velocity and the intensity of turbulence are in good agreement for both values. The main flow region in the dryer is almost coincident each other. The main (axial) flow rate increases remarkably by acompanying the recirculation flow in the axial direction of the dryer. which reaches a maximum value of about 1.7 times the inlet flow rate. The particle trajectories obtained in the calculated gas flow fields are influenced colisiderably by the recirculation flow.     

LEAFLASH SPRAY DRYER: INVESTIGATION OF THE ATOMIZATION PROCESS

The atomization process of the LEAFLASH spray dryer has been investigated by laser diffractometry and video imaging. The LEAFLASH atomizer is a particular pneumatic nozzle where the pressurized gas is the hot drying air. The drying and the atomization processes are interrelated in the spray dryer. Consequently the mixing of the liquid droplets and the drying medium is very efficient, permitting to work with short drying duration and reduced chamber volume. The mean diameter and the drop size distribution are measured at the outlet of the nozzle by laser diffraction. We studied the coupling effects of the air temperature (150 to 300° C) and pressure (1.20 to 1.50 bars abs) and of the dry matter content of the liquid feed (aqueous maltodextrin solution, 20 to 55% w/ w) on the droplets/ size distribution and on the general pattern of the spray. Analyses of video images of the generated spray give the general pattern of the spray and an estimation of the liquid velocity     

EXPERIMENTAL INVESTIGATION ON FLOW AND DRYING CHARACTERISTICS OF A VERTICAL AND SEMI-CYCLIC COMBINED IMPINGING STREAMS DRYER

Abstract

Flow characteristics of a vertical and semi-cyclic combined impinging streams dryer(VSCIS) was investigated. Results show that centrifugation and gravity have obvious influences on pressure drop and on momentum commutation between gas and particles in impingement zones. The effects of various operating parameters on water removal from particles have been studied experimentally. It is found that initial hot air temperature Tin, μ and initial moisture content of particles X₀ play important roles on water removal from particles. Based on the experimental data, dimensionless correlations for flow and drying characteristics in the system were obtained. VSCIS has shown to be a good way to overcome the shortcomings of single configuration of either vertical or semi-cyclic impinging streams. It can take full advantages of both arrangement to remove more water from particles.     

EXPERIMENTAL INVESTIGATION ON FLOW AND DRYING CHARACTERISTICS OF A VERTICAL AND SEMI-CYCLIC COMBINED IMPINGING STREAMS DRYER

Flow characteristics of a vertical and semi-cyclic combined impinging streams dryer(VSCIS) was investigated. Results show that centrifugation and gravity have obvious influences on pressure drop and on momentum commutation between gas and particles in impingement zones. The effects of various operating parameters on water removal from particles have been studied experimentally. It is found that initial hot air temperature Tin, μ and initial moisture content of particles X₀ play important roles on water removal from particles. Based on the experimental data, dimensionless correlations for flow and drying characteristics in the system were obtained. VSCIS has shown to be a good way to overcome the shortcomings of single configuration of either vertical or semi-cyclic impinging streams. It can take full advantages of both arrangement to remove more water from particles.     

FLOW VISUALISATION AND INSTANTANEOUS VELOCITY MEASUREMENTS OF SPRAY DRYER GAS AND SPRAY FLOWS USING PARTICLE IMAGE VELOCIMETRY

The technique of particle image velocimetry has been used to produce good quality instantaneous velocity maps of the gas and spray phases within a pilot plant co-current spray dryer. Good quality flow visualisation data provided by the use of the laser sheet as an intense source of illumination has indicated that the air and spray flows were characterised by an offset central jet with down flowing (right hand side) and up flowing (left hand side) wall streams. This is significantly different from what would normally be expected and it was suggested that this was possibly due to a maldistribution of the air phase on inlet to the dryer.     

AIR FLOW, TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

FLOW VISUALISATION AND INSTANTANEOUS VELOCITY MEASUREMENTS OF SPRAY DRYER GAS AND SPRAY FLOWS USING PARTICLE IMAGE VELOCIMETRY

ABSTRACT

The technique of particle image velocimetry has been used to produce good quality instantaneous velocity maps of the gas and spray phases within a pilot plant co-current spray dryer. Good quality flow visualisation data provided by the use of the laser sheet as an intense source of illumination has indicated that the air and spray flows were characterised by an offset central jet with down flowing (right hand side) and up flowing (left hand side) wall streams. This is significantly different from what would normally be expected and it was suggested that this was possibly due to a maldistribution of the air phase on inlet to the dryer.     

AIR FLOW,TEMPERATURE AND HUMIDITY PATTERNS IN A CO-CURRENT SPRAY DRYER: MODELLING AND MEASUREMENTS

ABSTRACT

In a co-current pilot plant spray dryer measurements were done of the airflow pattern (no spray) and the temperature and humidity pattern (water spray). These patterns were simulated with a computational fluid dynamics package (FLOW3D)

The measured air velocities showed large fluctuations. The measured and predicted flow pattern showed good agreement qualitatively, but the measured profiles showed less variation than the predicted ones

The measured temperatures and humidities showed good agreement in large areas of the dryer, but the agreement in the zone near the central axis leaves room for improvement.     

喷干塔五种燃煤方式的综合分析

本文根据实际使用效果,分析介绍了喷干塔五种燃煤方式的工作原理及特点,并从粉料工艺性能,燃煤适应性,操作及控制,建设投资,运行成本等方面进行了综合分析。     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

AN EXPERIMENTAL INVESTIGATION OF INITIATION AND CESSATION OF FLOW IN A TUBE FOR NEWTONIAN FLUIDS

An experimental investigation of sudden initiation and cessation of laminar flow in a tube following the opening and closure of a direct acting solenoid valve is reported for Newtonian fluids in the viscosity range 0.9 ≤ μ ≤ 39.5 centipoise. A non-contact probing Laser Doppler Anemometer and a high speed data logging system are used to make local axial velocity measurements at 85 tube diameters from the entrance to a test section, 1.36 cm I.D. and 1.4 meters long. Some qualitative measurements of the pressure gradient over the test section are also made.

The results show that for Newtonian fluids, with μ ≤ 27.1 cp, the sudden opening or closure of the solenoid valve is not equivalent to a step input in either pressure drop or flow rate. Both show overshoots, the magnitude of which decreases with increasing viscosity of the fluid. The normalized time for a 90% development or decay increases with the viscosity of the fluid. For fluids with μ ≥ 39.5 cp, the behavior appears to approach that due to a step input in pressure gradient.     

EXPERIMENTAL INVESTIGATION ON SOLAR DRYING OF FISH USING SOLAR TUNNEL DRYER

This paper presents field level performance of the solar tunnel dryer for drying of fish. The dryer consists of a transparent plastic covered flat plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using four d.c. fans, operated by two 40 watt solar modules. This dryer can be used to dry upto 150 kg of fish and three sets of full scale field level drying runs for drying silver jew (Johnius argentatus) fish were conducted in February-March, 1999. The temperature of the drying air at the collector outlet varied from 35.1 ° C to 52.2 ° C during drying. The fish was initially treated with dry salt and stacked for about 16 hours before drying. The salt treated fish was dried to a moisture content of 16.78% (w.b.) from 67% (w.b.) in 5 days of drying in solar tunnel dryer as compared to 5 days of drying in the traditional method for comparable samples to a final moisture content of 32.84%. In addtion, the fish dried in the solar tunnel dryer was completely protected from rain, insects and dust, and the dried fish was a high quality product.     

MODELLING GAS-SOLID FLOW IN A PNEUMATIC-FLASH DRYER

ABSTRACT

Investigations of aerodynamics of gas-solid flow in a pneumatic-flash dryer in semiindustrial scale have been carried out. Apparatus was composed of three elements with varying cross-sectional area connected together, i.e. expanding cone, decreasing cone and a vertical pipe with constant diameter. A mathematical model of the dryer is based on the continuity equations for both gas and solid phase and on differential equations for momentum balance of the gas-solid mixture and momentum balance of the solid phase. The model has been solved by means of Gear's numerical method. The effect of various empirical correlations for the solid-wall friction factor has been shown. Distributions, resulting from the model, for pressure, gas velocity, panicle velocity, voidage and residence time of panicle along the axis of apparatus have been presented. The results of numerical calculations have been verified on the basis of measurements in pan.     

EXPERIMENTAL STUDY OF RESIDENCE TIME IN A DIRECT ROTARY DRYER

Prediction of residence time in rotary dryers is useful for equipment design as well as for the right selection of operation conditions in order to obtain the optimal unit functioning.

An empirical relationship for residence time estimation that may be applied when the dryer slope is zero or different from it is presented in this work. It was derived from experimental testing carried out with biological origin particulated solids (fish and soya meal, sawdust) and from mineral origin (sand) in a pilot rotary dryer. The fitting degree of the experimental data to those predicted by reported equations was also established here.     

MODELLING GAS-SOLID FLOW IN A PNEUMATIC-FLASH DRYER

Investigations of aerodynamics of gas-solid flow in a pneumatic-flash dryer in semiindustrial scale have been carried out. Apparatus was composed of three elements with varying cross-sectional area connected together, i.e. expanding cone, decreasing cone and a vertical pipe with constant diameter. A mathematical model of the dryer is based on the continuity equations for both gas and solid phase and on differential equations for momentum balance of the gas-solid mixture and momentum balance of the solid phase. The model has been solved by means of Gear's numerical method. The effect of various empirical correlations for the solid-wall friction factor has been shown. Distributions, resulting from the model, for pressure, gas velocity, panicle velocity, voidage and residence time of panicle along the axis of apparatus have been presented. The results of numerical calculations have been verified on the basis of measurements in pan.     

SIMULATION OF SPRAY DRYING OF A SOLUTION ATOMIZED IN A PULSATING FLOW

Spray drying of NaCl solution was carried out under an intense oscillating flow field generated by a pulse combustor. A pulse combustion spray drying system was constructed. An optical analyzer was used to measure the particle diameter distribution of droplets atomized by a pulsating flow. The momentum, heat and mass transfer in both gaseous and particulate phases during spray drying inside the drying chamber were simulated using the computational fluid dynamics method. The simulated profiles of flow field, temperature and humidity of the gaseous phase, as well as the particulate phase, in the drying chamber were presented. The simulation showed changes of the flow field and particle trajectories in the drying chamber during one pulsating period. A large-scale vortex was observed in the upper part of the drying chamber because of the unstable state of flow field and particle trajectories. Short drying time and large evaporation rate are characteristics of pulsating spray drying. The influence of gas stream pulsation frequency on the drying process is also analyzed.     

滴流床反应器内脉冲流下动持液量实验

对气液强相互作用下滴流床反应器内的流体动力学进行了分析讨论 .实验测定了脉冲流流型下的床层平均动持液量 .考察了气液流率、液体黏度、填料材料等因素对动持液量的影响 .根据对滴流床反应器内流体流动机理的分析及实验结果 ,提出了关联脉冲流型式下动持液量的关联式 .该关联式能很好地关联实验数据 ,可用于预测温和型脉冲流下的动持液量